Pressure Leaf Filter: Types, Working Principles, And Key Differences

A pressure leaf filter is a widely used solid-liquid separation device in industry, mainly used for efficiently separating solid particles from liquids. Its core feature is that it works under pressure and uses movable leaf-shaped filter elements for filtration and slag discharge. In this article, Yuwei Filtration will explore the pressure leaf filter in depth, from its core mechanisms to the unique advantages of each type.

Types of Pressure Leaf Filters

Pressure leaf filters are mainly divided into two basic types according to their structure: vertical and horizontal.

1. Vertical Pressure Leaf Filter 

• Structural features: 
  • The tank body is a vertical cylinder (vertical type). 
  • The filter leaves are vertically suspended in the tank, usually fixed on the top liquid collection pipe. 
  • The slag discharge port is located at the bottom of the tank (equipped with a quick-opening bottom cover). 
• Typical applications:
  • non - stringent scenarios such as chemical industry, food industry, and general pharmaceutical industry.

2. Horizontal Pressure Leaf Filter 

• Structural features: 
  • The tank body is a horizontal cylinder (horizontal type). 
  • The leaves are installed horizontally or slightly inclined, fixed on the liquid collection pipe running through the tank. 
  • The slag discharge port is located on the side or bottom (controlled by a sliding valve / side door).
• Typical applications:
  • pharmaceutical industry (meeting GMP sterile requirements), fine chemical industry, solvent recovery, etc.

Working Principle of Pressure Leaf Filter

Regardless of the structure, the core process of the pressure leaf filter is pressure filtration + air blowing dehydration + reverse blowing discharge.

1. Feed Filtration: 

• Operation steps:

• • Seal the tank; pump the slurry into the tank under pressure; the liquid passes through the filter cloth to become filtrate, and the solid forms a filter cake. 

• Goal: Preliminary solid-liquid separation.

2. Blowing Dry / Pressing: 

• Operation steps:

• • Pass compressed air through the filter cake; (for pressing type) the diaphragm expands to mechanically squeeze the filter cake. 

• Goal: Deep dehydration to reduce the moisture content of the filter cake.

3. Reverse Blowing Discharge:

• Operation steps:

• • Open the slag discharge port; pass compressed air in the reverse direction; the filter cake breaks and falls off. 
• Goal: Automatically discharge dry slag.

4. Cleaning: 

• Operation steps: Inject cleaning liquid to circulate and rinse the filter cloth (started as needed).
• Goal: Restore filtration efficiency.

Differences in Working Principles of Different Types of Pressure Leaf Filters

From a technical perspective, the core differences in working principles between vertical and horizontal pressure leaf filters are mainly reflected in three aspects: first, the gas replacement efficiency during feeding; second, the tightness level during slag discharge; third, the auxiliary discharge method.

1. Differences in Feeding and Filtration Stages

Vertical type: 

•  Fast gas conversion:

During feeding, gas naturally floats up and is discharged through the top exhaust port, so the tank is quickly filled with slurry. 

• Uniform filter cake distribution:

The gaps between vertical leaves are consistent, and the gravity of the slurry helps in uniform distribution.

Horizontal type: 

•  Need for forced exhaust:

Horizontal tanks are prone to residual air traps. 

• Uneven filter cake thickness:

 The bottom of horizontal leaves is prone to material accumulation.

2. Differences in Blowing Dry / Pressing Stages

Vertical type: 

• High blowing dry efficiency:

The filter cake is vertically attached to the leaves, the resistance of air flow penetrating from top to bottom is small, and the liquid is easy to discharge. 

• Limitation in pressing:

Only affected by gas pressure, no additional mechanical extrusion.

Horizontal type: 

•  Need to prevent short circuit:

Horizontal filter cakes may produce air flow "channeling", so uniform air distribution or segmented pressure application is required. 

• Gravity-assisted dehydration:

The filter cake is located under the leaves, and gravity helps discharge the liquid at the bottom. Essential

3. Differences in Discharge Stage (Core Differences)

Vertical type:  

• Open exposure:

The bottom quick-opening cover needs to be fully opened, and the filter cake is exposed to the atmosphere. 

• Gravity - dominated:

After reverse blowing, the filter cake is discharged by free fall, with a fast speed. 

• Low safety:

High risk of exposure to toxic / flammable materials, not suitable for sterile environments.

Horizontal type: 

• Fully closed during the whole process:

Only partial slag discharge is carried out through the side narrow - gap sliding valve (or rotary valve), and the tank remains closed.  

• Active discharge:

After reverse blowing, the filter cake falls to the bottom of the tank, and a vibrator or scraper is needed to assist in pushing it to the slag discharge port.  

• Safe and controllable:

Supports inert gas protection, meets explosion - proof and sterile requirements, and realizes zero exposure of materials.

The vertical type achieves efficient discharge by means of gravity but sacrifices tightness; the horizontal type gains fully closed safety guarantee at the cost of structural complexity. The differences between the two are not about superiority or inferiority, but targeted solutions according to material risk, process requirements, and cost constraints.